This invention pertains to personal identification verifier apparatus and more particularly to such apparatus which utilizes signature pressure patterns and stylus movements in the identification process.
In many fields and particularly in personal identification fields such as access control, charge account, banking and credit card operations it is desirable to convert person's signature to electrical signals which are then used in a verification and/or identification process. It has been found that when a person writes his signature he not only generates a unique visual pattern on a record medium, but he also generates a unique pressure pattern. The uniqueness of the pressure pattern has been exploited to build verification systems. Typical systems are disclosed in U.S. Pat. Nos. 3,480,911, 3,563,097 and 3,618,019, for example.
Some of these systems use pens with strain gauge transducers therein while other systems employ pressure sensitive writing surfaces. The transducer pens generally are very expensive and delicate and suffer low gauge factor/sensitivity and significant hysteresis. In fact, most of such pens break down when subjected to a high impact shock which occurs from the forceful dotting of an "i." In addition, the pen and associated wire are difficult to shield electromagnetically and are subject to data interception. Finally, the pen which dangles from the end of a cable is subject to theft and vandalism.
On the other hand, pressure sensitive tablets, while not being subjected to the same set of problems, create their own set. In particular, the major problem is associated with the nonlinearity of the generated signals because of the extended writing surface. In order to linearize the signal, complex and delicate systems using springs, strain gauges and the like are employed. Even with these expensive solutions, such devices still suffer from relatively high hysteresis and marginal natural frequency.
In a previous attempt to solve these problems I invented an improved transducer system which is the subject matter of my U.S. Pat. No. 4,035,768, issued July 12, 1977. While that system performed with high accuracy it created a demand for even higher accuracies by measuring more variables.